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(also called heat production), the production of heat in an organism as a result of the transformations of energy in living cells. Thermogenesis is associated with the continuous biochemical synthesis of proteins and other organic compounds, with osmosis (the passage of ions through concentration gradients), and with the functioning of such muscles as the cardiac muscle, the smooth muscles of various organs, and the skeletal muscles. Even when the muscles are entirely at rest, such osmosis and functioning are considerable: a person of average weight and age in an optimal environmental temperature releases approximately 1 kilocalorie (4.19 kilojoules) per kg of body mass per hour. At rest, approximately 50 percent of all the body’s heat is produced in the organs of the abdominal cavity, mainly in the liver, up to 20 percent in the skeletal muscles and central nervous system, and approximately 10 percent, by the functioning of the organs of respiration and the circulation of blood. Thermogenesis is also called chemical thermoregulation.
In homeothermic animals, the thermogenesis per unit of body mass increases with decreasing body size. For example, in mice the thermogenesis per unit of body mass is eight to ten times greater than in man. Thermogenesis increases sharply during muscular activity, reaching ten times the level at rest. Thermogenesis increases by ten to 20 percent during the first few hours after the intake of food, owing to the dynamic effect of food. Moreover, in man and in homeothermic animals, thermogenesis increases during cooling. This defensive reaction is based on specific types of contractive activity of the skeletal muscles— cold-induced muscular tremor and thermoregulatory muscle tone. When thermogenesis exceeds heat elimination, hyperthermia occurs.
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Ivanov, K. P. Bioenergetika i temperaturnyi gomeostazis. Leningrad, 1972.
Hammel, H. “Regulation of Internal Body Temperature.” Annual Review of Physiology, 1968, vol. 30.
Lehninger, A. L. Bioenergetics. New York, 1965.
K. P. IVANOV